KR20200096844A - Light detection method - Google Patents

Abstract

The present invention relates to a method for detecting light for detecting light during a sub-frame 501 of a picture frame operation display. The sensing is performed during an adaptive observation window c that is determined depending on the duty cycle DC of the operation of the display. Calculations using the light sensed during the observation window (OWP) and light sensed during the sub-frame (ALLP) yield a value representing the amount of ambient light received.

Description

Light detection method

The present disclosure relates to a light sensing method. In particular, the present disclosure relates to a light sensing method comprising receiving light at a photosensitive element and operating a display. The method determines a value representing the amount of ambient light received.

Electronic devices often adapt the brightness of the display screen to the ambient light. The light sensor determines a signal indicative of the amount of ambient light so that the brightness of the displayed information can be adapted to the convenience of a person reading the display. Current displays, especially display screens in cell phones or smartphones, want to have a light sensor located behind the screen that controls the adjustment of the screen brightness by covering almost the entire surface of the front. However, in this case, the sensor receives the light generated by displaying the ambient light plus information.

Displays used in current smartphones alternately illuminate pixels by one picture frame. One picture frame may include several, for example, four sub-frames. The brightness is controlled by the duty cycle of the illumination of the pixels during the sub-frame. The low duty cycle has a short on-time and long off-time of the pixels to produce low brightness of the screen. The high duty cycle has a long on-time and short off-time of the pixel to produce high brightness.

In bezel-less smartphones, current sensors located behind the display screen measure ambient light during the additionally inserted off-time of the display. Because the time available for measurement is relatively short, the measurement process may not be sufficiently stable and may suffer from transient effects. In addition, transient effects from the surroundings, such as modulated light from bulbs, fluorescent lamps or LED lights, can affect the measurement.

Thus, there is a need for a more reliable measurement of ambient light in situations where an optical sensor is placed behind a display.

It is an object of the present disclosure to provide a method for detecting light useful for an optical sensor disposed behind a precise display screen.

According to the present disclosure, the above-mentioned object is achieved by a method according to the features of claim 1.

The method according to the present disclosure receives light in a photosensitive element such as a photoelectric device or a photodiode. The photodiode generates a current that can be measured and, depending on the case of measurement, is representative of the received light including ambient light and display light. Measurement of the current representing the amount of light received can be performed in several ways. One possibility is the use of a sigma-delta modulator that determines the current by a charge subtraction method and generates a stream of pulses whose density per time represents the amount of light received.

The display may operate on a frame-by-frame basis for a plurality of frames in which one picture frame includes a plurality of, for example, four sub-frames. In a sub-frame, information is displayed during the active period of the duty cycle, where the pixels of the screen are in the off-state during the inactive period of the duty cycle. Because these effects are so fast, the human eye does not perceive on/off modulation of the display of information. Thus, the brightness of the screen is controlled by the duty cycle that operates the pixels of the screen in sub-frames of the frame system. This operation is controlled by a pulse width modulation (PWM) signal.

The method according to the present disclosure requires two measurements. First, detection of light for a whole or full sub-frame, and second, detection of light during an observation window. A value representing the amount of ambient light received is achieved by calculating using two measurements.

The adaptive observation window, which depends on the actual duty cycle of the sub-frame's pulse width modulated signal, ensures that reliable measurements are performed at different operating states of the duty cycle. As a result of the adaptive measurement window, the detection process and calculation of ambient light is reliable without the need to affect the operation of the display, such as shut-off of the display for a small amount of time. Measurements can be performed in parallel and simultaneously with the operation of the display without disturbing the operation of the display. The method allows the sensor to be placed behind the display screen.

The observation window depends on the duty cycle of the presentation of information in the sub-frame. When the display screen is operated at low brightness, which means that the duty cycle of the illumination of the pixels in the sub-frame has a short active on-time and a long inactive off-time, the observation window is of the pulse width modulated signal. It is set to be at least active during the active phase of the duty cycle. Moreover, the observation window is slightly longer than the active phase of the duty cycle in that margin is added. In the case of such low display brightness or low duty cycle, the viewing window covers the active phase of the duty cycle and the transitional phase in addition to it.

When the display screen is operated at high brightness, meaning the duty cycle has a long active on-time and a short inactive off-time, the viewing window is set to be active during at least the inactive phase of the duty cycle of the pulse width modulated signal. Moreover, margins are also added to cover the transition phase. As a result, the measurement window measuring the light received in the sub-frame is set differently between a duty cycle higher than a predetermined rate and a duty lower than a predetermined rate. Indeed, the observation window is set differently for duty cycle rates lower than 50% and higher than 50%. Other predetermined rates of choosing between different viewing windows are also possible.

In one embodiment, depending on the duty cycle rate, the margin added to the active phase of the duty cycle or the inactive phase of the duty cycle is a transition from a higher amount of light to which a sensed light signal is received to a lower amount of light to be received. It is the transitional time representing the transition from an amount of light to a higher amount of light. It is useful to add both leading and trailing margins to achieve the observation window. This also ensures that the transition steps are evaluated by the sensing process. The detection time is longer and the transient effect is completely included in the detection result. In addition, the margins on both sides render the system insensitive to sensor mounting position changes in production.

In one embodiment, the sensing process comprises sigma-delta modulation of a sigma-delta analog-to-digital converter producing a stream of pulses “1” in which the amount of pulses or temporal density over a unit of time represents the amount of light sensed. . For example, a high pulse density indicates a large amount of light being sensed, and a low pulse density indicates a small amount of light being sensed. When the duty cycle of the sub-frame is at a lower rate, e.g., lower than 50%, the observation window is the time when the density of the pulses is high, which is the active phase of the duty cycle of the sub-frame, and also a lower It includes preceding and trailing transition steps comprising a transition from a pulse density to a higher pulse density and on the other hand from a higher pulse density to a lower pulse density. When the duty cycle of the sub-frame is at a higher rate, e.g., higher than 50%, the observation window is the time when the density of the pulses is low, which is the inactive phase of the duty cycle of the sub-frame, and also more on the one hand. It includes preceding and following transition steps from a high pulse density to a lower pulse density and on the other hand from a lower pulse density to a higher pulse density.

The number of pulses is counted during the observation window. Moreover, the number of pulses is counted for all or the entire period of the sub-frame. By calculation, only values for display light and only values for ambient light are calculated numerically. Specifically, a stream of pulses representing the amount of light received from light received by a photosensitive device such as a photodiode is generated. The detection of light during the sub-frame includes a first counting of pulses during the sub-frame. This counting is performed during and outside the observation window. Sensing of light during the observation window includes another, second counting of pulses during the observation window. Counting values obtained from the first and second countings are further processed to calculate a value representing the amount of ambient light received. The calculation can also use the value of the duty cycle of the viewing window and the value of the duty cycle of the operation of the display, the latter being used to achieve the desired brightness of the screen or display of information. The latter duty cycle is achieved by a pulse width modulated signal that operates the display.

In one embodiment, the sigma-delta modulation process includes an integrating capacitor that is charged by the current received from the photodiode. The voltage on the capacitor is compared to the threshold. When the threshold is reached or exceeded, a pulse "1" is generated and the charge charged to the capacitor is reduced by a fixed amount of charge supplied from the other capacitor and the integration process proceeds. The higher the current from the photodiode, the faster these steps occur and the pulses are denser in time units. The concept of a sigma-delta modulator is well known to those skilled in the art. The present disclosure regarding an adaptive observation window is useful in connection with a sigma-delta modulator, but the use of other integrated analog-to-digital conversion processes is also possible.

Other analog-to-digital conversions useful in the present disclosure may include charging the capacitor by photocurrent and comparing the charge or voltage on the capacitor to a reference charge or reference voltage to generate a signal or digital number representing the amount of light received. have.

Returning to the sigma-delta modulation concept, counting of pulses during a sub-frame results in a value for every pulse counted ALLP. Such counting includes counting during and outside the observation window. The additional counting of pulses during the adaptive observation window results in multiple pulses OWP. The duty cycle of the observation window (OW) can be calculated by dividing the active length of the observation window by the total period that is the sum of the active and inactive phases of the observation window signal. If the duty cycle is lower than a predetermined rate of, for example, 50%, the value representing the amount of light received during the active phase of the display duty cycle including display light plus ambient light is as follows:

DLP = (OWP-ALLP * OW) / (1-OW).

The value for ambient light ALP can be calculated by

ALP = ALLP-(OWP-ALLP * OW) / (1-OW) or

ALP = ALLP-DLP.

If the duty cycle is higher than a predetermined rate of, for example, 50%, the calculation further requires the value DC of the duty cycle of the pulse width modulated signal operation of the display so that the value DLP can be calculated as follows:

DLP = (ALLP * OW * DC-OWP * DC) /

(OW * DC + (1-DC)-OW).

Further, in this case, the values for ambient light ALP are as follows

ALP = ALLP-(ALLP * OW * DC-OWP * DC) /

(OW * DC + (1-DC)-OW) or

ALP = ALLP-DLP.

Since the observation window is active for a small amount of time in the range of the active phase of a lighting element such as a light bulb, fluorescent lamp or LED lamp, it is useful to perform sensing and counting processes for several consecutive sub-frames. . This reduces the intermodulation results of sensor output values caused by lighting systems operating based on the main frequency. In practice, the light modulation by the main frequency is 50 Hz or 60 　Hz. The display update rate may also be 60 Hz for one picture frame, which may contain 4 sub-frames inside the picture frame. It is useful to perform detection and counting for several picture frames and sub-frames, e.g. for the length of time of 6 picture frames, which means 24 sub-frames in this example. . This reduces or substantially averages the effect of the reception of the 50/60 Hz-modulated light received by the sensor.

Moreover, since the content of the picture to be displayed on the display screen or the image information to be displayed can be changed from the last sub-frame of the preceding picture frame to the first sub-frame of the subsequent picture frame, the first sub-frame of the picture frame It is useful not to start counting at. In order to avoid transitional effects from updating the information to be displayed, it is useful to start the sensing and counting processes in at least the second or third or fourth sub-frame of the picture frame. When detection is made for 24 sub-frames, the total measurement period will end at the last, for example the second, third or fourth sub-frame of the sixth picture frame.

It should be understood that both the foregoing general description and the foregoing detailed description are examples only and are intended to provide an overview or framework in order to understand the nature and features of the claims. The accompanying drawings are included to provide a further understanding and are incorporated into and constitute a part of this specification. The drawings illustrate one or more embodiments, and together with the specification serve to explain the principles and operation of the various embodiments. Identical elements in different figures of the drawings are denoted by the same reference symbols.

In the drawings:
1 shows a sample portion of a sequence of pulses received from a sigma-delta modulator;
2 shows a pulse sequence and an adaptive observation window for a high duty cycle;
3 shows a pulse sequence and an adaptive observation window for a low duty cycle;
4 shows counts and calculated values for a low duty cycle situation;
5 shows counts and calculated values for a high duty cycle situation;
6 shows a signal diagram for spreading several picture frames.

The present disclosure will now be described more fully herein after reference to the accompanying drawings showing embodiments of the present disclosure. However, the present disclosure may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will fully convey the scope of the disclosure to those skilled in the art. The drawings are not necessarily drawn to scale, but are configured to clearly illustrate the present disclosure.

In one embodiment, the light sensor is disposed behind or below the display of the smartphone. The light sensor serves to detect the level of incident light during operation of several stages and calculate the ambient light from it so that the brightness of the smartphone's display screen can be controlled to provide the user with a convenient appearance and readability. . The optical sensor includes circuitry that determines the amount of light incident on the photoelectric element in the sensor, such as a photodiode. In this embodiment, the sensor includes a sigma-delta modulator coupled to the photodiode to sense incident light.

The current generated by the incident light repeatedly charges the capacitor. In other words, the current from the photodiode is integrated by the capacitor. The capacitor voltage is compared to the threshold level. When the charge/voltage exceeds the threshold level, a pulse is generated and the charge on the capacitor is reduced by a predetermined reference charge. The capacitor is continuously charged by the diode current and the process described above is repeated again. If there is a bright light such that the diode current is high, the charging of the integrated capacitor is fast and the number of pulses generated by the sigma-delta modulator in time units is high. When the light intensity and diode current are low, the density of pulses generated in time units is low. Other principles of measuring diode current in an integrated manner, different from the sigma-delta modulator concept described above, may also be possible.

1 shows an exemplary bit-stream produced by the sigma-delta modulation process described above. The bit-stream 110 includes a section 111 of low density pulses, indicating that the light incident on the sensor has a low density. Section 112 contains high-density pulses, indicating that a large amount of light or light with high brightness is incident on the sensor. The bit-stream is followed by a section 113 of a low-density bit-stream followed by a section 114 of a high-density bit-stream, followed by a section 115 of a low-density bit-stream. The bit-stream is due to the transitional effect of the components and processes used and due to the ratio of the width of a single display line to the sensor window, the transitional portions 211, 212 between the high-density section and the low-density section. , 213, 214).

Alternating sections of higher and lower pulse density such as 111, 112, etc. are the result of the operation of the display screen in the described embodiment of the smartphone. The display is operated frame by frame, where one picture frame is subdivided into, for example, four sub-frames. Picture information to be displayed is updated from a picture frame to a picture frame. Picture information within a frame is displayed four times by sub-frames to increase picture quality. Within a sub-frame, the pixels on the screen are dark, illuminated for part of the sub-frame and blocked for the rest of the sub-frame. The relationship between the active portion and the inactive portion of the sub-frame is perceived as the brightness of the screen. When the active portion is short and the inactive portion is long, picture information displayed on the screen appears relatively dark. When the active part is long and the inactive part is short, the displayed picture information is bright. The brightness of the screen is set by the relationship between the active and inactive parts of the screen's illumination within a sub-frame of the screen's frame-wise operation. This operation is controlled by a pulse width modulation (PWM) control signal defined by the smartphone's processor. The pulse width rate or duty cycle of a pulse width modulated signal is the ratio between the active and inactive portions of the illumination of the screen during a sub-frame, which controls the brightness of the display.

During the active phase of the duty cycle, the lines of the display are illuminated in a continuous sequence so that the sensor placed behind the display receives light from adjacent lines in active phases such as 112 and 114 in addition to ambient light. During inactive phases such as 111, 113, 115, the light incident on the sensor comes from the surroundings of the smartphone when only ambient light is incident on the sensor. The ambient light may be natural light, sunlight or artificial light from bulbs, fluorescent lamps or LED lamps.

In order to adjust the brightness of the smartphone's display in response to the amount of ambient light in order to achieve a convenient appearance for the user, the sensor must determine the amount of ambient light. For example, low density pulse section 113 is a bit-stream representing ambient light sensed by the sensor, while high density pulse section 112 contains ambient light plus light sensed by the sensor. According to the embodiment described herein, the window detects the high density or low density portion of the bit-stream generated by the sigma-delta modulator and performs calculations to calculate the display light portion and the ambient light portion included in the bit-stream. To be generated in response to the duty cycle of the PWM display operation. This process will be described in more detail herein below.

2 shows the relevant signals used in the process according to this embodiment. 2 shows a bit-stream 301 having a high density pulse section 312 and leading and trailing low density pulse sections 311 and 313. The duty cycle of the display screen is represented as a bit-stream 301 by the relationship of the high density portion 312 over the entire period of the display cycle within a sub-frame. It should be noted that FIG. 2 does not fully illustrate the entire display cycle as only one representative high-density portion 312 is shown that is repeated periodically. Section 312 is caused by display generated light plus ambient light, and sections 311 and 313 are caused only by ambient light.

Figure 3 shows another light sensing situation where only a small portion 412 of the bit-stream has a low density with only ambient light. Leading and trailing portions 411, 413 are high density portions containing ambient light plus display generated light. As apparent from the comparison of FIGS. 2 and 3, the duty cycles of the display expressed as the relationship between the high-density pulse portions 312 and 411, 413 for the entire repetition period are the duty cycles of the PWM display operations of FIG. It differs in that it is lower than that of FIG. 3. These duty cycles result from a pulse width modulated (PWM) signal that controls the operation of the display in a sub-frame.

In accordance with the present disclosure, the observation window signal 302 is generated to evaluate counts of pulses. During the activation phase 320 of the observation window signal 302, the pulses of the bit-stream signal 301 are counted. All pulses in the bit-stream 301 that occur during the active observation window step 320 are counted by the counter. The observation window 320 is controlled by a pulse width signal that controls the duty cycle of the display operation. In the case shown in FIG. 2 with a low duty cycle of less than 50%, the viewing window 320 covers the high density pulse section 312 of the bit-stream. In the case shown in FIG. 3 with a high duty cycle of more than 50%, the viewing window 420 covers the low density pulse section 412. The pulses of the bit-stream 301 and 401 that occur during the presence of the active portion of the observation windows 320 and 420 are counted in the counter, respectively. Moreover, all pulses are counted inside and outside the observation window by other counters. This process may require at least two counters for the counting operation during the observation window and for counting inside and outside the observation window.

Thus, the process of this disclosure is adaptive in that it uses different viewing windows 320 and 420 depending on the current value of the duty cycle of the PWM display operation. For a low duty cycle as shown in FIG. 2 of less than 50%, the observation window 320 includes the active portion of the duty cycle and consequently a relatively short high density pulsed section 312 of the bit-stream 301. . When the duty cycle is more than 50% complementary, the viewing window 420 includes the inactive portion of the duty cycle of the display operation and includes the low density portion 412 of the bit-stream 401. This means that the counting and observation window of the corresponding pulses of the bit-stream is adaptive in that it is dependent from the value of the duty cycle of the display operation.

According to one aspect of the present disclosure, the adaptive observation window also includes margins 322, 323, 422, 423 added to the pulse width signal sections 321, 421. Margins include transition steps from a low density section to a high density section of a bit-stream such as 322, 423 and transitions from a high density section to a low density section of a bit-stream such as 323, 422. Transition sections are soft transitions in which the sigma-delta conversion process produces a gradual increase or decrease in the density of pulses from one density state to another. The inclusion of margins in the adaptive observation windows means that the observation windows contain a full amount of pulses generated by the display or a sufficient number of bit-stream pulses containing a complete phase of low pulse density that does not have pulses generated by the display. Ensure that they cover a large enough period to collect them. In one embodiment, the margin is a fixed value large enough to ensure that the entire transition step is covered by the observation window. For example, the margin may be a period of 25%, which is divided by 12.5% on both sides of the length of the pulse width signal section. For example, if the active portion of the pulse width signal is 5%, then the observation window including the margins occurs at 30%. If the active part of the pulse width signal is close to parity, such as 40%, the observation window occurs at 65%. The proper setting of the margin can be determined by simulation or experiment. The size of the margin may depend on the bandwidth of the sigma-delta conversion process, the ratio of the width of a single display line to the sensor window and other parameters. Moreover, the margin size can be configured in such a way that variances in the position of the sensor during production are eliminated.

With reference to FIGS. 4 and 5, calculations to be performed from the counting described with respect to FIGS. 2 and 3 are described. FIG. 4 shows a situation in which the display duty cycle is low, and FIG. 5 shows a situation in which the display duty cycle is high. A low duty cycle means a duty less than a predetermined value, eg less than 50%, and a high duty cycle means a duty greater than a predetermined value, eg, higher than 50%. 4 and 5 show count values and calculations for obtaining a display light portion and an ambient light portion.

Referring now to Figure 4, curve 501 shows a display pulse width modulation (PWM) signal with a duty cycle of less than 50%. The active phase (a) of the pulse width signal is short compared to the inactive phase (b), which is somewhat longer. The duty cycle of the pulse width modulated signal 501 is DC?=?a/(a+b). Signal 502 is a viewing window signal with an active phase (c) covering the active phase (a) plus margins added to the left and right of the pulse width signal 501. The inactive phase of the observation window signal is step (d). The pulse width of the observation window signal is OW = c/(c+d). Graph 503 shows the pulses from sigma-delta modulation in abstract form. All pulses ALLP for a period are the sum of the pulses OWP and XOWP counted during each, active phase (c) and inactive phase (d) of the observation window signal, i.e. during and outside the observation window. The number of pulses is ALLP = OWP + XOWP.

Referring now to FIG. 5, a situation with a pulse width duty cycle greater than 50% is shown. The pulse width signal 601 has a large active step (a) and a short inactive step (b). The active window c of the observation window signal 602 includes margins added to the left and right of the inactive step (b) plus the pulse width modulated signal 601. In the calculations for the duty cycle DC of the pulse width modulated signal (here, DCL = 1-DC), the observed window duty cycle OW and the bit-stream pulses ALLP are the same as the situation described in connection with FIG. 4. The calculations performed for both cases of less than 50% and greater than 50% pulse width modulation duty cycle are as follows:

1.PWM DC <50% (Fig. 4):

` ALLP = ALP + DLP (One)

OWP = ALP * OW + DLP (2)

From (1): ALP = ALLP-DLP (3)

(2) in (3): OWP = ALLP * OW-DLP * OW + DLP (4)

From (4): DLP = (OWP-ALLP * OW) / (1-OW) (5)

From (3): ALP = ALLP-K1 * DLP (6)

2. PWM DC> 50% (Fig. 5):

ALLP = ALP + DLP (7)

OWP = ALP * OW + DLP * (OW-DCL) / DC (8)

From (7): ALP = ALLP-DLP (9)

(8) in (9): OWP = ALLP * OW-DLP * OW +

DLP * (OW-DCL)/ DC(10) (10)

From (10): DLP = (ALLP * OW * DC-OWP * DC) /

(OW * DC + DCL-OW) (11)

From (3): ALP = ALLP-K2 * DLP (12)

In the above calculations, ALP are bit-stream pulses representing ambient light and DLP are bit-stream pulses representing display light. It should be noted that the formula contains the corresponding correction factors K1 and K2. In practice, K1 and K2 can be omitted, that is, K1 = K2 = 1. However, depending on the specific situation in the smartphone and depending on the components used, it may be useful to use a correction factor that takes into account reflections originating from lines close to the sensor when the sensor is behind the display screen. Reflections originate from neighboring lines and can be reflected off elements of the screen such as screen glass and entered into the photodiode. Correction factors can be used to remove this parasitic effect from the calculation. In any case, the correction factors K1, K2 are relatively close to 1 or 100%.

Although the present measurement process has been described in terms of bit-streams generated by sigma-delta modulation converters, it is possible that it is also used in other light sensing methods. In practice, any integrated analog-to-digital converter can be used. For example, the converter can operate based on charge and discharge capacitors and can evaluate analog values rather than bit-streams.

6 shows a chart of several related signals occurring in the method according to the invention at a higher system level. Several consecutive picture frames are shown, with the first picture frame and the last picture frame labeled as 710 and 711. One picture frame includes four sub-frames 720. One sub-frame is controlled by a pulse-width modulated signal PWM with a duty cycle of DC (Figs. 4 and 5). In current smartphones, picture information to be displayed is updated with a first sub-frame within a picture frame. The picture information is repeated four times in four consecutive sub-frames 720.

The display update cycle of modern smartphones is a 60 Hz picture frame repetition rate, where the picture frame is updated every 16.7 ms (milliseconds). The four PWM sub-frames are in one picture frame. In order to achieve an integration time of at least 50 ms to reduce the influence of the 50 Hz or 60 Hz light modulation, the measurement can be continued for 12 sub-frames. More preferably, the integration time may be at least 100 ms and the measurement continues for 24 sub-frames. The extension of the counting for 12 or 24 frames means that artificial light that can be modulated by 50 Hz or 60 Hz from a bulb, fluorescent lamp or LED lamp is substantially reduced or even removed by averaging OWP, XOWP counts. Guaranteed.

Signal 730 represents a bit-stream from the sigma-delta transform where the pulses are so dense that they are not individually visible in this level of representation. The measurement window 740 of 24 sub-frames is enabled to select consecutive sub-frames with a duration of 6 picture frames. As is apparent from FIG. 6, the selection window 740 selects the third sub-frame 721 from the first picture frame 710. As a result, the measurement window ends at the second picture frame 722 of the last picture frame 711. Counting of pulses OWP, XOWP (FIGS. 4 and 5) is additionally performed for 24 sub-frames selected by measurement window 740. Counting proceeds continuously for OWP and XOWP for 24 sub-frames. If counting for only 12 sub-frames (not shown in the figures) is required, the measurement window is configured such that a period of 3 picture frames is selected.

In order to avoid the influence of the change of display content information made in the first frame of the new picture frame, the measurement should not start with the first frame of the new picture frame. Instead, the measurement for 24 consecutive sub-frames should start with the second, third or fourth sub-frame of the picture frame, and correspondingly, the measurement is the first, second or second of the last selected picture frame. It ends with 3 sub-frames. That is the third sub-frame 721 of the first picture frame 710 in FIG. 6 as the first sub-frame in which the selection window 710 starts measuring and counting OWP and XOWP values for 24 sub-frames. ) Is the reason to choose. In this example, the measurement window is stretched for 24 sub-frames with a period of 6 picture frames. The 24 sub-frames are taken from 7 consecutive picture frames, with the first and last picture frames contributing only to a subset of their sub-frames. In general, the measurement should be 50 ms or a multiple of 100 ms, or preferably longer than 100 ms.

The present disclosure measures with an adaptive observation or measurement window. As a result, ambient light sensing can be performed for a wide range of pulse width modulation (PWM) duty cycles in which the display of information in a sub-frame of a frame-operated display screen is controlled. The adaptive measurement window can be extended with margins covering soft transitions from high pulse density to low pulse density and from low pulse density to high pulse density of the sigma-delta modulated pulse stream. Margins make the solution also insensitive to sensor variances in production. The overlap margin of OW to DC (see FIGS. 4 and 5) also includes sensor position differences in production. The measurement has high precision and covers a wide range of PWM duty cycle values. In fact, the measurement achieves better accuracy than previous measurement solutions, where the measurement can only take place in the off-step of the display.

It will be apparent to those skilled in the art that various modifications and variations may be made without departing from the spirit or scope of the present disclosure as defined in the appended claims. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the present disclosure may occur to those skilled in the art, this disclosure is to be construed as including all within the scope of the appended claims. Should be.

Claims (15)

In the light sensing method,
Receiving light at a photosensitive element and generating a signal (110, 301, 401) representing the amount of the received light;
Operating a display having at least one sub-frame (720, 501, 601) having duty cycles (501, 601) to display information having brightness depending on the duty cycle;
Sensing the light during the at least one sub-frame (720, 501, 601);
Sensing the light during a viewing window (320, 420, 502, 602), the viewing window being determined depending on the duty cycle (501, 601); And
Calculating a value indicative of the amount of ambient light received from the light detected during the viewing window and from the light detected during the sub-frame. The method of claim 1,
The duty cycle comprises a first portion (a) in which the display is operated to emit light and a second portion (b) in which the display is operated not to emit light, wherein
When the duty cycle has a first rate lower than a predetermined rate, the observation window is during at least one margin (322, 323) added to the first portion and the first portion of the duty cycle (321). Determined to be active,
When the duty cycle has a second rate higher than the predetermined rate, the observation window is at least one margin (422, 423) added to the second portion and the second portion of the duty cycle (421). Determined to be active during. The method of claim 2,
The at least one margin (322, 323, 422, 423) is a transition time representing a transition from a higher amount of light (312, 411) to a lower amount of light (313, 412) at which the signal is received, and the The method, wherein the signal comprises at least one of a different transition time indicating a transition from a received lower amount of light (311, 412) to a higher amount of light (312, 413). The method according to claim 2 or 3,
Generating a signal indicative of the amount of light received comprises:
Generating a stream of pulses (110, 301, 401) in which the temporal density of pulses represents the amount of light received;
here,
When the duty cycle has the first rate, the observation window 320 has a first margin comprising the transition time 322 from lower density pulses to higher density pulses and a higher density. Is determined to include a second margin comprising the transition time 323 from pulses of
When the duty cycle has a second rate, the observation window 420 is a first margin comprising the transition time 422 from higher density pulses to lower density pulses and a lower density. And a second margin comprising the transition time (423) from pulses to higher density pulses. The method of claim 4,
The step of generating a signal indicative of the amount of light (110, 301, 401) received comprises generating a current in a photosensitive element and generating a stream of pulses by a sigma-delta modulation process, wherein ,
The step of sensing the light during the observation window includes counting the pulses generated during the observation window,
Wherein the step of sensing the light during the sub-frame includes another step of counting the pulses generated during the sub-frame. The method of claim 5,
The step of generating a stream of pulses by a sigma-delta modulation process comprises:
Incorporating the current in a capacitive element;
Generating a pulse when the charge stored in the capacitive element exceeds a threshold value;
And then subtracting a predetermined amount of charge from the charge stored in the capacitive element and continuing to incorporate the current into the capacitive element. The method according to claim 5 or 6,
In response to a pulse width modulated signal, when the duty cycle (DC) of the operation of the display is lower than the predetermined rate, calculating a value DLP representing the amount of received light from an indication of information:
Counting the pulses during the observation window as OWP;
Counting the pulses during the sub-frame as ALLP;
It includes the step of calculating the following formula,
DLP = (OWP-ALLP * OW) / (1-OW)
Wherein OW represents the duty cycle of the observation window. The method of claim 7,
The step of calculating the value ALP representing the amount of the received ambient light is the following equation:
ALP = ALLP-(OWP-ALLP * OW) / (1-OW) or
ALP = ALLP-DLP
Comprising the step of calculating. The method according to any one of claims 5 to 8,
In response to a pulse width modulated signal, when the duty cycle (DC) of the operation of the display is higher than the predetermined rate, calculating a value DLP representing the amount of received light from the indication of the information:
Counting the pulses during the observation window as OWP;
Counting the pulses during the sub-frame as ALLP;
It includes the step of calculating the following formula,
DLP = (ALLP * OW * DC-OWP * DC) /
(OW * DC + (1-DC)-OW),
Wherein OW represents the duty cycle of the viewing window and DC represents the duty cycle of the operation of the display. The method of claim 9,
The step of calculating the value ALP representing the amount of the received ambient light is the following equation:
ALP = ALLP-(ALLP * OW * DC-OWP * DC) /
(OW * DC + (1-DC)-OW) or
ALP = ALLP-DLP
Comprising the step of calculating. The method according to any one of claims 1 to 10,
Sensing the light during multiple sub-frames 720 and detecting the light during multiple viewing windows occurring within the multiple sub-frames to reduce ambient light modulation caused by the main frequency. Including, how. The method according to any one of claims 5 to 10,
Counting the pulses during a number of sub-frames 720 to reduce ambient light modulation caused by the main frequency, and counting the pulses during a number of observation windows occurring within the plurality of sub-frames. Counting. The method of claim 12,
Operating the display includes displaying information in a plurality of picture frames 710 and 711, each frame including two or more sub-frames 720, and a plurality of sub-frames During 720, the counting of the pulse starts with a sub-frame occurring second or after the first picture frame 710 among the plurality of picture frames 710 and 711, and the pulse during a plurality of observation windows. The counting of the plurality of picture frames ends with a sub-frame occurring first or after the last picture frame 711 of the plurality of picture frames. The method according to any one of claims 2 to 10,
Wherein the predetermined rate of duty cycle is 50%. The method according to any one of claims 1 to 14,
Receiving light from an optoelectronic device and performing sigma delta modulation on the current generated by the optoelectronic device to generate a stream of pulses (110, 301, 401) representing the amount of received light;
Counting the pulses during at least one sub-frame (501, 601, 720);
When the duty cycle of operating the display during the at least one sub-frame is lower than 50%, then:
Counting the pulses during a viewing window (320) comprising an active portion (321, a) of the duty cycle and a margin portion (322, 323) before and after the active portion;
When the duty cycle of operating the display during the at least one sub-frame is higher than 50%, then:
Counting the pulses during an observation window (420) comprising an inactive portion (421, b) of the duty cycle and a margin portion (422, 423) before and after the inactive portion;
Counting during sub-frame 720 and continuing the counting during measurement window 740 for several subsequent sub-frames, thereby adding the respective counts for the several subsequent sub-frames. step;
The counts from the sub-frames and the counts from the viewing windows and the sub-frames to achieve a value for the light received from the indication of the information and/or the received ambient light. Performing a calculation using values for the duty cycle and the duty cycle of the observation windows;
And adjusting the duty cycle of further occurring sub-frames to achieve an adjusted brightness of the indication of the information that is adjusted to the calculated ambient light.

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